The present invention relates to whitening agent particle compositions, more particularly, to whitening agent compositions in the form of discrete particles, to the process for making them. In this regard, U.S. applications Ser. No. 08/616,570 now U.S. Pat. No. 5,714,452; Ser. No. 08/616,208 now U.S. Pat. No. 5,714,456; are hereby incorporated by reference in their entirety. The whitening agent particle compositions made by the process described below are suitable for admixture with powder laundry detergents, bleaching powders and other powder laundry products. Thus, the present invention also relates to a powder detergent containing discrete whitening agent particles.
It is known to add whitening agents to washing detergents in order to enhance the whiteness and brightness of the washed textiles. In particular, fluorescent whitening agents (FWAs) counteract the yellowing of cotton and synthetic fibers. FWAs are adsorbed on fabrics during the washing process. FWAs function by absorbing ultraviolet light, which is then emitted as visible light, generally in the blue wavelength ranges. The resultant light emission yields a brightening an whitening effect, which counteracts yellowing or dulling of the fabric. If, however, the whitener, particularly a fluorescent whitener, is incorporated in powdered detergents in the customary manner, they have an exceedingly undesirable drawback. Frequently, they cause a deterioration in the bulk appearance of the detergent. Unattractive, yellow or greenish-yellow powders of reduced commercial value are produced. Without being bound by any particular theory, it is believed that the whitening agents react with the detergent surfactants causing the agent to change forms and thereby cause the bulk appearance of the detergent to change. This reaction appears to be particularly prevalent when the detergent contains a substantial amount of nonionic surfactant.
One solution that has been proposed is to select a fluorescent whitening agent that may be more stable in a detergent containing a high nonionic surfactant concentration. The drawback to such whitening agents is that they lack cold water performance and they are expensive.
Another solution that has been proposed is reported in U.S. Pat. Nos. 4,298,490 and 4,309,316 to Lange et al. In these patents, a fluorescent whitener such as a bis-styrylbiphenyl, a bis-triazoylstilbene or naphthotriazolylstilbene type, is dissolved or dispersed in a mixture of water and a polymer (polyvinyl alcohol or polyvinyl pyrrolidone) and then added to the detergent slurry which is then later dried. Alternatively, the whitener solution or dispersion may be spray dried, suspended in water, added to the detergent slurry and then spray dried. These methods, however, require many processing steps prior to incorporation into a detergent slurry. Therefore, there is a need for a powder detergent that contains a whitening agent and which does not suffer from discoloration of the bulk detergent upon storage.
It has now been discovered that a whitening agent composition can be formed into discrete particles so that they can advantageously be added to, for example, a powder detergent composition.